Blastomycosis, one of the principal systemic mycoses, often produces a progressive pulmonary disease, but the factors that account for immune failure and resistance during infection with Blastomyces dermatitidis infection are ill defined. We created a WI-1 knockout of B. dermatitidis that is attenuated and controlled in a murine model of primary pulmonary infection. Its administration to mice vaccinates them against re-infection and evokes sterilizing immunity. We propose here to use the isogenic attenuated and wild-type strains and mouse models developed in the last funding period to define the cellular and molecular bases of immune failure and resistance in experimental pulmonary blastomycosis. We hypothesize: that B. dermatitidis subverts generation of immune T-cells in a nonimmune host, leading to progressive infection. In a vaccinated host, T-cells mediate resistance, and show plasticity in the requirements of T-cell subsets for generation and maintenance of vaccine immunity and memory. Our specific aims are to: (1) Decipher the role of the immunosuppressive cytokine transforming growth factor-beta (TGF- beta) in failure of T-cell immunity during progressive primary infection, and the participation of CTLA-4, a negative regulator of T-cell activation, during TGF-beta-induced cellular immune suppression. (2) Delineate differential mechanisms - cytokines (IFN-gamma, TNF-alpha), cytolysis, and direct antimicrobial activity - by which CD4+ and CD8+ T-cells mediate vaccine immunity to B. dermatitidis, and requirements for CD28 co- stimulation and IL-12 signaling in generating and maintaining these recall immune responses. (3) Identify and clone antigens that protective T-cells recognize in vitro from expressed products of a B. dermatitidis cDNA library, and in T-cell immunoblots of a crude, protective cell-wall membrane antigen, and demonstrate that the cloned recombinant antigens confer protective immunity in vivo to B. dermatitidis. Understanding mechanisms of immune failure and resistance to fungi will assist in planning vaccine and treatment strategies in healthy people, and in patients with impairments of host defense such as AIDS.